(1) Field of the Invention
This invention relates to a scanning electron microscope or similar equipment, and more particularly to a scanning electron microscope or similar equipment provided with a magnetic pole piece to decrease the magnetic flux leaked through an opening of a lower pole of an electromagnetic objective lens.
(2) Description of the Prior Art
A conventional scanning electron microscope is accompanied by a drawback that, as shown in FIG. 1, its resolution is limited to an order of 60-70 .ANG. or so because it is designed to place a specimen c below the lower pole b of an electromagnetic objective lens a and it thus has a long focal distance and a large aberration coefficient.
It may be conceivable to place the specimen c in the vicinity of the lens center g of the objective lens a (here, the lens center g is located above the lower pole (b) for the purpose of improving its resolution. However, such a measure is known to involve the following problems:
(1) The diameter of the opening of the lower pole b has to be great to permit a disposition of the specimen c at a point above the lower pole b. Accordingly, when the specimen c is placed below the lower pole b, more magnetic flux tends to leak through the thus-enlarged opening of the lower pole b, thereby deleteriously affecting the collection of secondary electrons and magnetizing the magnetic specimen, and, corollary to this, lowering the S/N ratio(signal-to-noise ratio) and consequently deteriorating the quality of an image to be obtained. PA1 (2) The crossing point between the scanning beam and optical axis cannot be changed even when the position of the specimen c is varied. Accordingly, it is impossible to select optimum lens conditions in accordance with the position of the specimen c. This results in a poor image quality. PA1 (1) A specimen can be placed either below the lower pole of the objective lens or in the vicinity of the lens center of the objective lens as the operator desires, thereby making the scanning electron microscope or similar equipment applicable for varied purposes. PA1 (2) A specimen image of good quality can always be obtained even if a specimen is placed at different locations as above.
In FIG. 1, letters d, e and f designate a detector, amplifier and cathode-ray tube respectively.